This study is designed to establish a cohort of women aged 30-54 in whom several known risk factors for the development of breast cancer have been identified and in whom oral contraceptive use, cigarette smoking and permanent hair dye use are being assessed. The cohort would then be followed for several years during which time the occurrence of a number of cancers and coronary events would be monitored. The population is made up of all married, registered nurses from 11 large states in the United States. Name and address of each woman was obtained from a registry provided by the American Nurses' Association. Approximately 180,000 women were invited to participate, and we would expect to have approximately 112,000 women enrolled in the prospective portion of the study. Each woman completes a detailed mail questionnaire which includes family, personal and medical history. The immediate goal of this research will be the analysis of the prevalence data with respect to disease association with the exposure factors under study.